woocommerce-gift-product.php

<?php

function bbloomer_add_gift_if_sku_added_cart( $passed, $product_id, $quantity ) {
  global $woocommerce;
 
  /* enter array of SKUs that give gift */
  $skuswithgift = array('KCF-N-ATC', 'armsup');
 
  /* enter SKU of product gift */
  $giftsku = 'ajandek';
 
  /* enter name of coupon that gives 100% discount for specific product gift */
  $coupon_code = 'kedvezmeny';
 
  $product = wc_get_product( $product_id );
 
  if ( 
    ( $product->get_sku() && in_array( $product->get_sku(), $skuswithgift ) ) ||
    has_term( 'kategoria-slug', 'product_cat', $product_id )
  ) {
    WC()->cart->add_to_cart( wc_get_product_id_by_sku( $giftsku ) );
    wc_add_notice( __( 'Az ajándék terméket a kosárba helyeztük!', 'woocommerce' ), 'success' );
    $woocommerce->cart->add_discount( $coupon_code );
  }
  
  return $passed;
}
 
add_filter( 'woocommerce_add_to_cart_validation', 'bbloomer_add_gift_if_sku_added_cart', 10, 3 );